1. Field of the Invention
The present invention relates to a substrate for mounting a high frequency device, and more particularly, to a high frequency device mounting substrate suited to mount a frequency filter or a transmission-receiving branching filter (hereinafter referred to as a duplexer) serving as a high frequency device employed for a mobile communications apparatus.
The present invention relates to a communications apparatus on which the high frequency device mounting substrate is carried.
The present invention relates to a method of evaluating the characteristics of a high frequency device mounted on the high-frequency device mounting substrate.
2. Description of Related Art
In recent years, for frequency filters such as surface acoustic wave filters employed for mobile communications apparatuses such as cellular phones, requests that they should be small in size and light in weight, loss low inside passbands, be high in attenuation outside the passbands, and steeply change in characteristic from the inside to the outside of the passbands have become strong.
For duplexers that separate signals in transmission-side frequency bands (e.g., on the side of relatively low frequencies) and signals in receiving-side frequency bands (e.g., on the side of relatively high frequencies), requests that they should be small in size and light in weight, loss low in transmission bands and be high in attenuation in receiving bands in transmitting frequency filters within the duplexers, and loss low in receiving bands and be high in attenuation in transmission bands in receiving frequency filters within the duplexers have been also made. In the duplexers, it has been requested that isolation characteristics from transmission terminals to receiving terminals should be good in order to prevent transmission signals from leaking from the transmission terminals to the receiving terminals. As the duplexers, smaller-sized devices having low frequency band-side frequency filters, for example, serving as transmitting frequency filters and high frequency band-side frequency filters, for example, serving as receiving frequency filters integrated therein have been requested.
If high frequency devices that do not meet the above-mentioned requests are used for communications apparatuses, unnecessary radio signals are transmitted or received. Therefore, the qualities of the received radio signals may be degraded, and problems such as jamming to other radio communications apparatuses may occur.
In order to evaluate the characteristics of the above-mentioned high frequency devices such as the frequency filters and the duplexers, the high frequency devices have been carried on mounting substrates for evaluation to measure and evaluate whether or not desired characteristics are obtained.
Since the measurement and evaluation must be accurately made, connection between the high frequency devices and high frequency device mounting substrates and connection between high frequency device mounting substrates and coaxial connectors for connecting the high frequency device mounting substrates and coaxial cables connected to measuring equipments must be respectively firmly made with reliable conductivities ensured using solder.
FIG. 22 is a schematic perspective view showing a general high frequency device mounting substrate, and a high frequency device and a coaxial connecter that are connected thereto.
In the high frequency device mounting substrate, a required electrical circuit is formed of a conductor on a surface of a circuit board 50 having a plurality of insulator layers (not shown) laminated therein and having ground conductor layers (not shown) formed in their inner parts.
The electrical circuit comprises terminal electrodes (not shown) for mounting a high frequency device 41 to be evaluated, signal electrodes 23 and ground electrodes 24 for connecting a coaxial connector mounted so as to connect a cable connected to a measuring equipment and the high frequency device mounting substrate, and a signal line 2 for connecting the terminal electrode for the high frequency device 41 and the signal electrode 23 to each other.
A grounding effect may, in some cases, be increased by providing a through hole 47 penetrating the insulator layers in the circuit board 50 and also providing a conductor layer on an inner surface of the through hole 47 to electrically connect the ground conductor layers to one another, to reduce the parasitic inductance of the ground electrode 24.
The coaxial connector generally comprises a center conductor 44 for transmitting a signal, an outer peripheral conductor 45 surrounding the center conductor 44 and grounded, and an insulating member for insulating the center conductor 44 and the outer peripheral conductor 45. The center conductor 44 has a shape projecting from the insulating member such that it can be connected to the signal electrode 23 in the high frequency device mounting substrate and has a thickness conforming to the width of the signal electrode 23.
In order to assemble the respective members as shown in FIG. 22, cream solder is first applied to terminal electrodes formed on the circuit board 50, the high frequency device 41 having electrodes provided at its position corresponding to the terminal electrodes is carried thereon, and the high frequency device mounting substrate and the high frequency device 41 are connected to each other by reflowing, and the signal electrode 23 and the ground electrode 24 and the center conductor 44 and the outer peripheral conductor 45 are then respectively connected to each other using wire solder and a soldering iron.
The coaxial connector is connected to the coaxial cable connected to the measuring equipment, to measure the characteristics of the high frequency device 41.
In order to remove the coaxial connector from the high frequency device mounting substrate, the high frequency device mounting substrate must be heated to a temperature at which solder is melted (200° C. to 300° C.) to remove the high frequency device 41 using tweezers or the like.
In recent years, the high frequency devices have been progressively reduced in size and weight and correspondingly, the heat capacities of the devices themselves have been reduced, so that heat resistance has been degraded. When the coaxial connectors must be mounted and removed, as described above, therefore, there have been requests to complete mounting and removal thereof in a shorter heating time period than the conventional working time period.
Furthermore, even in the case of not only making measurement and evaluation, as described above, but also carrying high frequency device mounting substrates on communications apparatuses such as base stations and terminals to actually put the high frequency device mounting substrates into practice, the coaxial connectors for connecting the high frequency device mounting substrates and other circuit components must be firmly connected to the high frequency device mounting substrates using solder. When the connection is weak, the certainty of conductivity is lost, so that the reliability of the operations of the high frequency devices are degraded.
Therefore, an object of the present invention is to provide a high frequency device mounting substrate capable of satisfactorily exhibiting the characteristics of a carried high frequency device.
Another object of the present invention is to provide a high frequency device mounting substrate capable of ensuring firm connection with a coaxial connector and capable of simply removing the coaxial connector.
Still another object of the present invention is to provide a high frequency device characteristics evaluating method in which the characteristics of a high frequency device mounted on a high frequency device mounting substrate can be evaluated with high reliability.